The invention relates to switching regulators and more particularly to over-current detectors which monitor the current delivered by a switching regulator and provide a signal for disabling the regulator when the current exceeds a threshold value.
In high speed data processing systems, microcircuits are used to reduce the physical size of the system and to increase the operating speed. These microcircuits are built in modules each of which may replace a large number of circuits using discrete circuit components. Each of these microcircuit modules requires as much power as several circuits using discrete components so that the power required in a single cabinet of a data processing system using microcircuit modules is several times as large as the power required in a single cabinet using discrete components when the two cabinets have the same physical size. In addition, high speed microcircuits usually use a much smaller value of d.c. voltage than circuits employing discrete components. For example, in many high speed microcircuits the required d.c. voltage may be less than 5 volts. This voltage must be well regulated to provide a constant value of d.c. voltage for the microcircuits otherwise variations in d.c. voltage may produce error signals in the data processing system.
Many of the power supply systems employ switching regulators to provide the low value of well regulated voltage for the data processing systems. The a.c. voltage from a power supply line is converted to a relatively large value of unregulated d.c. voltage at a plurality of locations in the data processing system. This relatively large value of unregulated d.c. voltage can be converted to a relatively small value of d.c. voltage by the switching regulators at various locations in the data processing systems. Each of the switching regulators may employ a transformer, a pair of silicon controlled rectifiers and a source of signal to convert the unregulated d.c. voltage, such as 150 volts, to an accurately regulated voltage, such as 5 volts. The silicon controlled rectifiers are employed as switches between the source of unregulated d.c. voltage and the transformer. The silicon controlled rectifiers are located on the "high" voltage side of the transformer where the current and power losses in these rectifiers are low thereby causing the switching regulator to have a high degree of efficiency. The regulated d.c. voltage obtained from a secondary winding on the transformer is supplied to a pair of voltage output terminals. The transformer provides isolation between the regulated d.c. voltage and the source of unregulated d.c. voltage so that a short circuit in a silicon controlled rectifier will not cause damage to the microcircuit modules which provide the load on the switching regulator.
A signal source is coupled to the voltage output terminals of the switching regulator and develops trigger signals whose frequency is determined by the value of voltage at the voltage output terminal. The trigger signals are coupled to the silicon controlled rectifiers in the switching regulator and cause these rectifiers to deliver energy through the transformers to output filter capacitors which are connected to the voltage output terminal. The signal source senses any change in the value of the trigger signals delivered to the switching regulator. This change in frequency of the trigger signals causes a change in the "duty cycle" of the switching regulator. The duty cycle is a duration of time that energy is delivered to the output filter capacitors compared to the total duration of time between trigger signals. This change in the frequency of the trigger signals and in the duty cycle causes a change in the quantity of energy which the switching regulator delivers to the output filter capacitor so that the voltage at the output terminal returns to the original value.
It is desirable to monitor the current which the switching regulator delivers to a load and to provide a signal which will disable the regulator when the current delivered exceeds a threshold value. It is also desirable that the threshold value of this current be adjustable so that the switching regulator can be used with different loads which may require different values of current. Because previous systems required shutdown of the system to adjust the threshold value of current, adjustments were infrequently made. Therefore, it is still further desirable that the threshold value of current be adjustable without requiring a shutdown or otherwise interrupt the data processing system being supplied.
Accordingly, it is an object of the present invention to provide a power supply which allows for adjusting the over-current detection threshold level without interrupting the system.
This and other objects of the present invention will become more apparent when taken in conjunction with the following description and attached drawings, wherein like characters indicate like parts, and which drawings form a part of the present application.